1. Field
Embodiments of the invention relate to Ga—P—S glass compositions. The glass compositions may transmit infrared radiation. Infrared-transmitting glasses have application in, for example, infrared (IR) windows, waveguiding fibers, and as host glasses for luminescent dopants, for example, rare earth dopants.
2. Technical Background
Infrared radiation is the portion of the electromagnetic spectrum just below red light in terms of frequency. Infrared-transmitting materials have many applications. For example, in the field of astronomy, the earth's atmosphere does not scatter infrared radiation as much as visible light. Thus, special filters that block all but infrared rays can be used to obtain precise astronomical images without the scattering associated with visible light. Transmitted infrared radiation can also be used, for example, in detecting the positions of objects or people in the absence of visible light. This property has been used in military applications, for example, in infrared sensors.
Infrared-transmitting glasses, such as those disclosed in commonly owned U.S. Pat. No. 5,240,885, transmit radiation well into the infrared portion of the electromagnetic radiation spectrum due to their low phonon energy. These glasses can be used, for example, for the fabrication of efficient lasers, amplifiers, and up converters when doped with the appropriate rare earth dopants.
Since metal-sulfur bonds are generally weaker than metal-oxygen bonds, sulfide glasses exhibit lower phonon energies than oxide glasses and, therefore, transmit radiation further into the infrared region of the electromagnetic radiation spectrum. Accordingly, sulfide glasses may have the potential of being host materials for rare earth metals for applications such as those described for the glasses of U.S. Pat. No. 5,240,885.
However, many sulfide glasses are dark in color and, consequently, may not be suited for some of the above applications inasmuch as such a host glass, rather than the rare earth element, would tend to absorb the radiation.
One exemplary sulfide glass, arsenic sulfide, is transparent to radiation in the long wavelength range of the visible portion of the radiation spectrum as well as far into the infrared region and, hence, would appear to be a suitable host glass for rare earth metals. Nevertheless, rare earth dopants have been found to be relatively insoluble in arsenic sulfide glasses.
Rare earth dopants are known to be very soluble in most oxide glasses and their apparent insolubility in arsenic sulfide glasses has been conjectured to be due to the gross structural dissimilarity existing between the latter and oxide glasses. Arsenic sulfide glasses are believed to consist of long chains and layers of covalently bonded pyramidal AsS3 groups, whereas oxide glasses typically comprise a three-dimensional network of relatively ionically bonded MO4 tetrahedra, where M is a so-called network-forming metal such as silicon, phosphorus, aluminum, etc. Rare earth dopants are readily accommodated in these ionic network structures where they can compensate charge imbalances that arise from the presence of two or more network-forming metals, for example, aluminum and silicon in aluminosilicate glasses.
Commonly owned U.S. Pat. No. 5,392,376 discloses a system of sulfide glasses which exhibits good transparency in both the visible and infrared portions of the electromagnetic spectrum, and which possesses a relatively ionic three-dimensional structure, comprises gallium sulfide glasses. In contrast to arsenic sulfide glasses, the structure of these glasses is based upon a three-dimensional linkage of corner sharing GaS4 tetrahedra. Rare earth metals are readily soluble in these glasses.
Binary AsP sulfide glasses have been described in the Journal of Non-Crystalline Solids in the articles “Vibrational Spectra and Structure of As—P—S Glasses” and “A Glass-Forming System With Compound-Forming Tendency: AS4S6—P4S10”. However, the glasses described in the articles are Ga-free.
Commonly owned U.S. Pat. No. 6,277,775 describes Ge-rich GeAs sulfide glasses containing P2S5 and optionally Ga2S3 or In2S3 as useful host glasses in which rare earth dopants can also be efficiently dispersed.
It would be advantageous to have additional Ga—P—S glass compositions which are transparent in the infrared portion of the electromagnetic spectrum and which can be effectively doped with rare earth metals. Also, it would be advantageous to have Ga—P—S glass compositions which are also transparent into the visible portion of the electromagnetic spectrum having increased durability.